Carbon black has historically been the reinforcing agent of choice for rubber-based products such a tires and extruded and molded goods. Carbon black, which is produced by the thermal decomposition of oil and natural gases, greatly enhances mechanical strength and resistance to abrasion, and as in the past has been an economically attractive approach to improving the physical properties of rubber products. However, the increasing demand for other oil or gas-derived petrochemicals combined with a decreasing supply of oil and natural gas has prompted searches for a carbon black replacement.
Reinforcing silica's higher costs and poor performances has previously prevented it from competing with carbon black as a reinforcing agent for rubber. However, with recent and projected oil and gas price increases amorphous and fine particle-size silicas have become economically competitive with carbon black. A major effort to make reinforcing silica competitive with carbon black on a performance basis has evolved as a result of these changing economical factors. One approach is the incorporation into the rubber recipe of reinforcing promoters or coupling agents to effectively bond the silica to the rubber. It has now been found that pyridines having sulfur-containing side groups can act as coupling agents for vulcanizable rubber compositions and greatly enhance the stress-strain moduli of such compositions.
Accordingly an object of this invention is to provide vulcanizable rubber compositions exhibiting improved product properties.
Another aspect of this invention to provide novel rubber reinforcing promoters.
A further object of this invention is to provide improved vulcanizable silica-containing rubber compositions.
A further object of this invention is to provide reinforcing promoters that will effectively bond the reinforcing materials to rubber.
Other objects, aspects as well as the several advantages of the invention will be apparent to those skilled in the art upon reading the specification and the appended claims.